1. Technical Field
The present invention relates to a vacuum brake force booster comprising, in a booster housing, a vacuum chamber of a constant pressure, a working chamber of a variable pressure, and a control valve located in a control valve housing. One end of the control valve housing protrudes from the booster and is protected by a boot. On one end, the boot is sealingly fixed to the booster housing through a spacer. On its opposite end, the boot is sealingly secured to a piston rod serving as a control valve actuator.
2. Description of the Prior Art
In conventional brake force boosters of the afore-described type, the air required for ventilating the work chamber is passed through pedal-sided openings in the boot into the control valve housing. Although this way of ventilating is very simple, it usually means that the air is taken from the passenger cabin, thus creating substantial noise and causing inconvenience to the passengers.
Another brake force booster is shown in German patent application Ser. No. P 39 00 446.3. In that booster, only the portion of the booster housing facing the control valve housing is surrounded by a sheet metal tube. The boot is secured to the tube in order to draw in air. Manufacture and assembly of the tube are costly and complex. Moreover, the weight of the brake force booster is increased.